BaCd₂P₂—A Defect Resistant "GaAs"

Zintl phosphide BaCd₂P₂ (BCP) has recently received attention as a promising solar cell absorber. In this work, we present a comparative study of the optical properties of BCP and GaAs, providing a theoretical explanation for the excellent photovoltaic performance of BCP. Despite having much lower purity, BCP exhibits similar photoluminescence (PL) response, open circuit voltage, and radiative emission efficiency as high-purity GaAs. Further, by combining PL with first-principles defect calculations using Density Functional Theory, we identified the impact of prominent point defects in the two materials. BCP contains a lower density of its dominant deep nonradiative recombination center, P_Cd, compared to GaAs, whose dominant trap is As_Ga. Moreover, both BCP and GaAs show PL emissions from radiative point defects. The radiative defect emission in BCP likely involves V_Ba and is less detrimental than the radiative defect in GaAs, which we identified as B_As. Further, we characterize the mechanisms behind the optical transitions in the PL of BCP and GaAs; this revealed that V_Ba is likely part of a donor-acceptor pair. Our results suggest a high degree of impurity and defect tolerance in BCP compared to GaAs, making it an easily synthesizable, efficient solar absorber.